Novel photographic processes to produce precipitating nuclei in situ by electrolysis



R F W. CIECIUCH NOVEL PHOTOGRAPHIC PRbCESSES TO PRODUCE PRECIPITATING NUCLEI IN SITU BY ELECTROLYSIS EXPOSURE Filed Jan. 11. 1956 H IMPREGNATION ELECTROLYSIS INVENTOR.

M ATTORNEYS United States Patent 3,549,363 NOVEL PHOTOGRAPHIC PROCESSES T0 PRODUCE PRECIPITATING NUCLEI IN SITU BY ELECTROLYSIS Ronald F. W. Cieciuch, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation'of Delaware Filed Jan. 11, 1966, Ser. No. 519,886 Int. Cl. G03c 5/54 US. Cl. 96-29 17 Claims ABSTRACT OF THE DISCLOSURE Photographic processes for forming a silver image by diffusion transfer in which a soluble silver complex formed as a function of development of an exposed silver halide emulsion is reduced to image silver in the presence of silver-precipitating nuclei to form the silver transfer image, wherein the silver-precipitating nuclei are generated in situ by electrolysis.

This invention relates to photography and, more particularly, to a novel procedure for preparing images in silver by diffusion transfer.

Generally speaking, dilfusion transfer processes for preparing images in silver involve the steps of developing an exposed silver halide emulsion with an aqueous alkaline processing composition containing a silver halide developing agent and a silver halide solvent; reducing exposed silver halide to silver to form a negative silver image; forming from unexposed silver halide a soluble silver complex; and transferring an imagewise distribution of this soluble silver complex to a positive print layer or receiving layer where a fixed positive image in silver is formed.

In such diffusion transfer processes, it is common practice to employ a silver precipitating agent, or a combina tion of such agents, to accelerate the transfer process and/ or to influence the amount and character of the silver deposited on the receiving layer. These agents, often referred to as silver precipitating nuclei or as fogging agents, promote the reduction of the silver halide in the soluble silver complex to image silver without requiring the action of light.

As is disclosed, for example in US. Pats. No. 2,698, 237; 2,698,238; 2,698,245; and 2,765,240, all issued to Edwin H. Land, these silver precipitating agents may be present in the receiving layer; or, in lieu thereof, they may be incorporated in the processing composition, as disclosed, for example, in US. Pat. No. 2,662,822, also issued to Edwin H. Land.

A primary object of this invention is to provide a novel system for forming silver images by diffusion transfer.

Another object is to provide a novel system wherein the silver precipitating nuclei are formed in situ in the developing composition during processing of the exposed silver halide emulsion.

Still another object is to provide a novel system wherein the silver precipitating nuclei and the hydroxyl ions necessary to initiate development of an exposed silver halide emulsion are generated in situ in the processing composition at some time subsequent to applying the processing composition between the exposed photosensitive emulsion and a superposed image-receiving layer.

Yet another object is to provide novel electrolytic development processes for accomplishing the aforementioned objectives.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

FIG. 1 is a diagrammatic representation or flow sheet illustrating the invention; and

FIG. 2 is a partially schematic perspective view of one electrolytic system useful in the practice of this invention.

According to the present invention the silver precipitating nuclei employed in the preparation of the silver transfer image are generated in situ in the processing composition by impressing an electric charge at some time subsequent to applying the processing composition to the exposed silver halide emulsion.

It has been found quite unexpectedly that if the processing composition comprises an electrolytic solution containing an ingredient or combination of ingredients which upon impressing a suitable electric charge will form silver precipitating nuclei, dense silver transfer images may be obtained.

It will be appreciated that such ingredients, including the reaction products thereof generated by impressing the electric charge, as well as the electrolyte or combination of electrolytes employed in the processing composition should be photographically innocuous, i.e., should not be harmful or should not materially hinder the development process, although these ingredients may provide some additional function in the development and/ or formation of a transfer image in silver having the desired characteristics.

Useful electrolytes which would be photographically innocuous will be readily apparent to those skilled in the art and hence such materials per se comprise no part of this invention. As examples of useful electrolytes, mention may be made of the alkali metal sulfites, bisulfites, chlorates, chlorides, sulfates, etc.

The class of ingredients for providing the silver precipitating nuclei includes substance which, upon impress ing the electric charge will provide ions which, in the processing fluid, will in turn form the desired silver precipitating nuclei. One useful group of such ingredients comprises sulfur-containing compounds which, upon impressing the electric charge, will provide sulfide ions which in turn react with a portion of the silver halide to form silver sulfide, a heretofore known silver precipitating agent. A particularly useful class of sulfur containing compounds for this purpose are the sodium thiosulfates, e.g., sodium, potassium, ammonium, Zinc thiosulfate, etc. As examples of other useful sulfur-containing compounds, mention may be made of the thiocyanates, e.g., sodium and potassium thiocyanate.

In addition to the foregoing ingredients, the processing composition also contains a silver halide developing agent and a silver halide solvent, e.g., any of the silver halide developing agents and solvents commonly employed in diffusion transfer processes for preparing silver transfer images.

519,885 filed concurrently and now US. Pat. 3,362,823.

In the preferred embodiment, the hydroxyl ions are also generated in situ since this further minimizes the number of ingredients in the processing composition.

It will be appreciated that the processing composition may also contain other ingredients such as those recited in the aforementioned patents, e.g., viscous film-forming reagents, stabilizers, etc., performing their known functions.

It will also be appreciated that any of the aforementioned ingredients may be present initially in either the photosensitive element containing the silver halide emulsion or in the image-receiving element containing the receiving layer.

In preparing silver transfer images, a photosensitive element comprising a silver halide emulsion is exposed, impregnated with a processing composition of the foregoing description and thereafter the impregnated photosensitive element is subjected to an electric charge while in superposed relationship with a print-receiving element to form a transfer image in silver having a good D In known manner, the exposed silver halide is developed and an imagewise distribution of unexposed silver halide is transferred to the superposed print-receptive element wherein, with the aid of the silver precipitating nuclei, this imagewise distribution is reduced to image silver to provide the transfer image. This sequence of steps is shown schematically in FIG. 1.

This present invention is particularly adaptable to automatic systems for document duplication and the like, wherein the photosensitive element or film assembly containing the same is advanced from an exposure station to an impregnation station and finally to an electrolysis station to provide the desired reproduction of the original subject matter.

One useful electrolysis system or device for practicing the invention is illustrated in FIG. 2. As shown therein,

a pair of rollers 10' and 11 of a conductive material, such as .steel, are connected by leads 13 and 14, respectively, to a suitable source of electric current 15 which may, for example, be a 'battery. By way of illustration, roller 11 is shown to be cathodic while roller 10 is anodic. A suitable current is impressed as the photographic assemblage 12 including the previously impregnated photosensitive element and a superposed print-receiving element is advanced between the rollers, thus causing a direct electric current to flow through assemblage 12, thereby generating the precipitating nuclei in situ and in turn forming the desired silver transfer image.

It will be appreciated that the amount of current needed and speed of advancement of assemblage 12 through the rollers may vary widely and the selection of the particular operating conditions will be apparent to those skilled in the art.

As was mentioned previously, in a preferred embodiment a nonalkaline processing composition is employed and the hydroxyl ions necessary to initiate development are also formed in the electrolysis step.

For purposes of illustrating the present invention in greater detail, there will be described hereinafter its applicability to photographic systems such as are'described and claimed in copending application Ser. No. 519,995 filed concurrently in the name of Edwin H. Land, as a continuation-in-part of application Ser. No. 368,622 filed May 19, 1964, and application Ser. No. 519,884 filed concurrently in the names of Edwin H. Land and Leonard C. Farney, as a continuation-in-part of application Ser. No. 368,621 filed May 19, 1964.

As is disclosed in these applications, a photographic film assembly including a layer containing a light opacityproviding material is exposed, e.g., to a light source on the same side of the support for the film assembly as the layer of opacity-providing material and is then processed to form a negative image and a positive transfer image in a stratum situated above the layer of opacityproviding material. This material is present in an amount sufiicient for masking effectively the negative image but not in an amount sufiicient to preclude photoexposure of the light-sensitive material in the film assembly, so that there is formed a composite print which contains both a negative and a positive image but which is viewable by reflection as a positive reproduction of the original subject matter. In application Ser. No. 519,995, the layer of material is situated over a layer containing a lightsensitive silver halide emulsion; while in application Ser. No. 519,884, the material is situated in the same layer as the light sensitive silver halide emulsion and may also be present in a second layer over the layer containing the silver halide emulsion.

In any of the film assemblies described and claimed in the aforementioned latter two copending applications, silver precipitating nuclei may be contained in an outer layer comprisig a silver-receptive stratum, or, in lieu thereof, these nuclei may be present initially in the processing composition.

It will be apparent that in applying the present invention to the photographic products and processes described and claimed in the latter two applications, the silver precipitating nuclei are instead generated in situ in the processing composition after the film assembly is impregnated with the developing composition.

The following examples show by way of illustration and not by way of limitation the practice of this invention.

EXAMPLE 1 A photographic film assembly comprising a support having thereon, in order, a first layer containing a lightsensitive silver halide emulsion and a material and a second layer containing a material substantially equivalent to the film assembly described in Example 2 of the aforementioned application Ser. No. 519,884 was exposed for two seconds and the exposed sheet was passed at a rate of 0.3 in./sec. through a processing bath containing the following proportions of ingredients:

Water-550.0 cc.

Sodium sulfite-11.2 g. Hydroquinone4.0 g. Metol1.2 g.

Sodium thiosulfate-2.0 g.

The thus-wetted sheet was then passed between a pair of roller-electrodes, such as is illustrated in FIG. 2, at a charge of 15 volts and at a rate of 0.15 in./sec. to form a dense silver image viewable as a positive reflection print.

Similar results were obtained employing processing compositions containing hydroquinone alone, Metol alone, or 4,6-diamino-o-cresol as the developing agent.

EXAMPLE 2 Example 1 was repeated except that the wetted sheet was passed between the roller-electrodes at a charge of 35 volts and at a rate of 0.3 in./sec. to provide a silver image comparable to that obtained in Example 1.

EXAMPLE 3 Example 1 was again repeated except that the processlng bath contained the following proportions of ingredients:

Water-5 5 0.0 cc.

' Sodium sulfite--11.2 g.

Sodium hydroxide-21 g. Hydroquinone-4.0 g. Metol-1.2 g.

Sodium thiosulfate2.0 g.

Following electrolysis in the manner described in Example 1 a comparable silver image was obtained.

EXAMPLE 4 Substitution of 15 g. of sodium sulfate decahydrate (Na SO .10H O) for sodium sulfite in the processing composition of Example 1 followed by electrolysis in the same manner provided a good silver image viewable as a positive reflection print.

EXAMPLE 5 Substitution in the process of Example 1 of the following processing composition:

Water-550.0 cc.

Sodium sulfate (decahydrate)l5 .0 g. Hydroquinone4.0 g.

Sodium thiocyanate2.0 g.

gave a good silver image of somewhat lesser density.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a difiusion transfer process wherein a photosensitive element comprising a light-sensitive silver halide emulsion is exposed to form a developable image, said exposed photosensitive element is contacted with an aqueous processing composition to develop said image and to form an imagewise distribution of a soluble silver complex and said soluble silver complex is transferred, at least in part, by imbibition, to a stratum where it is reduced to image silver in the presence of silver precipitating nuclei to form a silver transfer image; the improvement which comprises generating said silver precipitating nuclei in situ by electrolysis at some time subsequent to contacting said exposed photosensitive element with said processing composition.

2. In a diffusion transfer process wherein a photosensitive element comprising a light-sensitive silver halide emulsion is exposed and developed with an aqueous alkaline processing composition containing silver precipitating nuclei to reduce exposed silver halide to image silver while at substantially the same time forming an imagewise distribution of a soluble silver complex and said imagewise distribution is transferred at least in part, by imbibition, to a superposed stratum where it is reduced to image silver to form a silver transfer image; the improvement which comprises impregnating said exposed light-sensitive emulsion with an aqueous processing composition including a material which upon impressing a direct electric current is capable of forming said silver precipitating nuclei and thereafter passing a direct electric current between said stratum and said impregnated emulsion while in superposition, whereby to generate in situ said silver precipitating nuclei.

3. A process as defined in claim 2 wherein said passage of current is effected by passing said emulsion and said superposed stratum between a pair of electrodes.

4. A process as defined in claim 3 wherein said electrodes comprise a pair of rollers.

5. A process as defined in claim 2 wherein said material comprises a sulfur-containing compound which, upon impressing said electric current, will form sulfur ions in said processing composition.

6. A process as defined in claim 5 wherein said sulfurcontaining compound is a thiosulfate.

7. A process as defined in claim 6 wherein said thiosulfate is an alkali metal thiosulfate.

8. A process as defined in claim 5 wherein said sulfurcontaining compound is a thiocyanate.

9. A process as defined in claim 2 wherein said processing composition is non-alkaline and hydroxyl ions are also generated in situ by said passage of current whereby to develop said negative image and to form said soluble silver complex.

10. A process as defined in claim 2 wherein said impregnation is effected by spreading said processing composition in a substantially uniform layer between said emulsion and said stratum.

11. A process as defined in claim 2 wherein said impregnation is effected by superposing said stratum on said emulsion and permeating said stratum with said processing composition.

12. In a photographic process wherein a layer containing a light-sensitive silver halide emulsion is exposed through a layer of a light opacity-providing material positioned thereover to form a developable image and said exposed emulsion layer is contacted with a developing composition to form a negative image in said lightsensitive layer and an imagewise distribution of soluble silver complex in terms of unexposed areas of said emulsion is transferred to a stratum above said layer of said material wherein it is reduced to image silver in the pres ence of silver precipitating nuclei to form a positive transfer image, said layer of said material being present in an amount sufficient for masking effectively said negative image while at the same time providing a background for said positive image thereover, thereby providing a composite print viewable by reflected light as a positive image; the improvement which comprises providing in said developing composition an electrolytic solution containing a material which upon impressing a direct electric current is capable of forming said silver precipitating nuclei, impregnating said exposed emulsion with said developing composition and thereafter passing a direct electric current therethrough, whereby to generate in situ by electrolysis said silver precipitating nuclei.

13. A process as defined in claim 12 wherein said contacting step is effected by permeating said processing composition through said layer of said opacity-providing material to said emulsion.

14. A process as defined in claim 12 wherein said processing composition comprises an aqueous non-alkaline electrolytic solution containing a silver halide developing agent and a silver halide solvent, and hydroxyl ions are also generated in situ by said electrolysis step whereby to develop said negative image and to form said soluble silver complex.

15'. A process as defined in claim 12 wherein said electrolysis step is effected by passing said two layers between a pair of electrodes. 16. In a photographic process wherein a layer containmg a light-sensitive silver halide emulsion and a light opacity-providing material is exposed to form a develop able image and said exposed layer is contacted with a developing composition to form a negative image in said layer and an imagewise distribution of soluble silver complex in terms of unexposed areas of said emulsion which is transferred to a stratum above said layer where it is reduced to image silver in the presence of silver preclpitating nuclei to form a positive transfer image on said stratum, said material being present in an amount suflicient for masking effectively said negative image while at the same time providing a background for said positive image thereover, thereby providing a composite print viewable by reflected light as a positive image; the improvement which comprises providing in said developmg composition an electrolytic solution containing a material which upon impressing a direct electric current is capable of forming said silver precipitating nuclei, impregnating said exposed emulsion with said developing composition and thereafter passing a direct electric current therethrough whereby to generate in situ by electrolysis said silver precipitating nuclei.

17. A process as defined in claim 16 wherein said processing coinposition comprises an aqueous non-alkaline electrolytic solution containing a silver halide develop- References Cited UNITED STATES PATENTS Land 9629 Land 9629 Land 9629 Land 9624 Viro 96 3 Baxendale et a1. 204-92 3,313,625 9/1967 Ryan 9629 3,335,007 8/1967 De Haes.

FOREIGN PATENTS 1,375,405 9/ 1964 France 204-92 GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner 10 Us. 01. X.R. 

